12 Aug 2022
12 Aug 2022
Status: this preprint is currently under review for the journal ACP.

Chemically distinct particle phase emissions from highly controlled pyrolysis of three wood types

Anita M. Avery1, Mariam Fawaz2, Leah R. Williams1, Tami Bond3,4, and Timothy B. Onasch5 Anita M. Avery et al.
  • 1Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA 01821, USA
  • 2Department of Civil and Environmental Engineering, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA
  • 3Department of Mechanical Engineering, Colorado State University, Ft Collins, CO USA
  • 4Department of Civil and Environmental Engineering, Colorado State University, Ft Collins, CO 80521, USA
  • 5Center for Sensor Systems and Technology, Aerodyne Research, Inc., Billerica, MA 01821, USA

Abstract. Wood pyrolysis is a distinct process that precedes combustion and contributes to biomass and biofuel burning gas phase and particle phase emissions. Pyrolysis is defined as the thermochemical degradation of wood, the products of which can be released directly or undergo further reaction during gas-phase combustion. To isolate and study the processes and emissions of pyrolysis, a custom-made reactor was used to uniformly heat small blocks of wood in a nitrogen atmosphere. Pieces of maple, Douglas fir and oak wood (maximum 155 cm3) were pyrolyzed in a temperature-controlled chamber set to 400, 500, or 600 °C. Real time particle phase emissions were measured with a Soot Particle Aerosol Mass Spectrometer (SP-AMS) and correlated with simultaneous gas phase emission measurements of CO. Particle and gas emissions increased rapidly after inserting a wood sample, remained high for tens of minutes, and then dropped rapidly leaving behind char. The particulate mass loading profiles varied with elapsed experiment time, wood type and size, and pyrolysis chamber temperature. The chemical composition of the emitted particles was organic (C, H, O), with negligible black carbon or nitrogen. The emitted particles displayed chemical signatures unique to pyrolysis and notably different from flaming or smoldering wood combustion. The most abundant fragment ions in the mass spectrum were CO+ and CHO+, which together made up 23 % of the total aerosol mass on average, whereas CO2+ accounted for less than 4 %, in sharp contrast with ambient aerosol where CO2+ is often a dominant contributor. The mass spectra also showed signatures of levoglucosan and other anhydrous sugars. The fractional contribution of m/z 60, traditionally a tracer for anhydrous sugars including levoglucosan, to total loading (f60) was observed to be between 0.002 and 0.039, similar to previous observations from wild and controlled wood fires. Atomic ratios of oxygen and hydrogen to carbon, O : C and H : C as calculated from AMS mass spectra, varied between 0.41–0.81 and 1.06–1.57, respectively, with individual conditions lying within a continuum of O : C and H : C for wood’s primary constituents: cellulose, hemicellulose, and lignin. This work identifies the mass spectral signatures of particle emissions directly from pyrolysis, including f60 and CO+/CO2+ ratio, through controlled laboratory experiments in order to help understand the importance of pyrolysis emissions in the broader context of wild and controlled wood fires.

Anita M. Avery et al.

Status: open (until 07 Oct 2022)

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Anita M. Avery et al.

Anita M. Avery et al.


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Short summary
Pyrolysis is the thermal decomposition of fuels like wood, which occurs during combustion or as an isolated process. During combustion, some pyrolysis products are emitted directly, while others are oxidized in the combustion process. This work describes the chemical composition of particle-phase pyrolysis products in order to inform both the uncombusted emissions from wild fires, and the fuel that participates in combustion.